Abstract adapter from operated to
managed client connections.
Read and write methods are delegated to the wrapped connection.
Operations affecting the connection state have to be implemented
by derived classes. Operations for querying the connection state
are delegated to the wrapped connection if there is one, or
return a default value if there is none.

This adapter tracks the checkpoints for reusable communication states,
as indicated by markReusable and queried by
isMarkedReusable.
All send and receive operations will automatically clear the mark.

Connection release calls are delegated to the connection manager,
if there is one. abortConnection will
clear the reusability mark first. The connection manager is
expected to tolerate multiple calls to the release method.

getSSLSession

Obtains the SSL session of the underlying connection, if any.
If this connection is open, and the underlying socket is an
SSLSocket, the SSL session of
that socket is obtained. This is a potentially blocking operation.
Note: Whether the underlying socket is an SSL socket
can not necessarily be determined via ManagedClientConnection.isSecure().
Plain sockets may be considered secure, for example if they are
connected to a known host in the same network segment.
On the other hand, SSL sockets may be considered insecure,
for example depending on the chosen cipher suite.

markReusable

Marks this connection as being in a reusable communication state.
The checkpoints for reuseable communication states (in the absence
of pipelining) are before sending a request and after receiving
the response in its entirety.
The connection will automatically clear the checkpoint when
used for communication. A call to this method indicates that
the next checkpoint has been reached.
A reusable communication state is necessary but not sufficient
for the connection to be reused.
A route mismatch, the connection being closed,
or other circumstances might prevent reuse.

unmarkReusable

Marks this connection as not being in a reusable state.
This can be used immediately before releasing this connection
to prevent its reuse. Reasons for preventing reuse include
error conditions and the evaluation of a
reuse strategy.
Note:
It is not necessary to call here before writing to
or reading from this connection. Communication attempts will
automatically unmark the state as non-reusable. It can then
be switched back using markReusable.

setIdleDuration

Sets the duration that this connection can remain idle before it is
reused. The connection should not be used again if this time elapses. The
idle duration must be reset after each request sent over this connection.
The elapsed time starts counting when the connection is released, which
is typically after the headers (and any response body, if present) is
fully consumed.

releaseConnection

Releases the connection with the option of keep-alive. This is a
"graceful" release and may cause IO operations for consuming the
remainder of a response entity. Use
abortConnection for a hard release. The
connection may be reused as specified by the duration.